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BrewCalc
How much yeast does this batch need?
The usual target is 0.75 million cells per millilitre per degree Plato for ales and about double that for lagers, because cold fermentation slows reproduction. Under-pitching a lager is one of the most common causes of sluggish, off-flavoured fermentation.
Too few cells forces the yeast through extra growth cycles before fermentation proper, and that stress produces esters, fusel alcohols, and diacetyl. Pitching enough healthy yeast is the cheapest quality improvement available to a homebrewer.
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OpenLast updated: August 2026
Yeast Packs Needed
1.88
0.75 M cells/mL/°P suits most ales; double it for lagers.
What you entered
Convert gravity to degrees Plato
(1.05 - 1) x 1000 / 4= 12.5 deg PCells required (million cells/mL/deg P)
0.75 x 20,000 mL x 12.5= 187,500 millionIn billions of cells
187,500 / 1000= 187.5 billionPacks of yeast needed
187.5 / 100 billion per pack= 1.875Result
Yeast Packs Needed: 1.88